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Cutting ground prong on 120volt pedal.


 
3/18/2005 5:48 PM
Humbucker
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Cutting ground prong on 120volt pedal.
I have a couple of stompboxes that are powered by a 120volt cord, inside of these pedals there's a small stepdown transformer. There seems to be a fair bit of noise added because of ground loops though.  
 
I was reading somewhere that you can cut the ground going to the pedals as long as the amp is still grounded, this gets rid of the ground loop problem. I know for a fact that this will really lower the noise issue but is it dangerous even though there's still a ground going through the cords and jacks back to the amp?
 
3/20/2005 8:21 AM
Steve Dallman
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If you are concerned about safety, buy yourself a GFCI adapter and plug your rig into that. Before getting kicked out of church (a story for another day) I was in charge of all the musical equipment and PA. I was forced to use ground lifts EVERYWHERE because of ground loop hum. The fire department was insistent that I take all the lifts out.  
 
Looking for a solution, I wired all the outlets with GFCI circuits. (Ground Fault Circuit Interrupters)  
 
The next inspection, they were satisfied.  
 
I only had one instance of an interrupter popping. In a tube bass preamp I build, one of the rF caps in the power supply started leaking. It was not audible and didn't affect operation of the preamp, but there was enough leakage to throw the protector. The amount of leakage was barely measurable.  
 
Another "trick" I used was to lift the ground and wire a cap between the line ground and the equipment ground. I would use a high voltage handling cap with anwhere from a .01uF to .1uF, depending on what I had available.  
 
Electricians are pretty clueless about wiring for sound installations. The last remodelling gave me a new soundroom. Because of the rF problems at our location (1/2 mile from a major AM and FM station's transmitting towers) I tried everything I could think of. After the room was roughed in, I stapeled screen over all the 2X4's before they drywalled it, and the screen was grounded. I don't know if my "cage" helped at all, but I had no rF problems in the new room. I should have located COPPER screen, but the room was quiet, despite the breaker boxes and main AC feed being on the other side of the wall.
 
3/20/2005 8:50 AM
KB
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Another thing that really matters is if the room or AC is two prong or three prong. Noise really gets magnified in two wire systems especially if other electronics are on like tv's, monitors, (computer)flourescant lights ect... and it can travel from down the road too as far as ten miles. Three wire systems are far superior and will have much less gorund loops however, in some situations you just have to lift grounds to keep everything happy in lieu of safety. I like Steves fix with the GFIC and Peavey uses the cap trick in their gear with a polarity sensitive switch that goes negative,zero and positive (-0+) for reversing mainly two wire systems that could be wired either way. Audiophiles however tend to forget about safety when it comes to getting the right tone and noiseless sound. But if you take your chances to often one day it WILL get you. So take Steves advice and shell the bucks for the GFIC.,  
 
KB
 
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